The present invention relates to a modular, programmable patient care system. Specifically, the present invention relates to an apparatus and method for a power management system for the modular, programmable patient care system.
Patient care systems containing multiple infusion pumping units and sensing devices such as blood pressure monitors and pulse oximeters are known in the medical field. For example, U.S. Pat. No. 5,713,856 to Eggers et al. discloses a modular, programmable patient care system comprised of an interface unit removeably attached to a plurality of patient functional units. The interface unit provides an interface between the user and the system, and may be either an advanced interface unit with a high level of interface functionality or a basic interface unit with a lower level of interface functionality. These units may be interchanged so as to provide increased flexibility, safety, and cost-effectiveness to the user. Each interface unit has interface ports for the uploading and downloading of information such as drug libraries, drug infusion profiles, system configuration values, and event history. As patient functional units are added to the interface unit, power requirements increase because each functional unit draws current from the power supply of the interface unit.
The patient care system has a battery backup to supply power when AC power fails or when not connected to AC power, such as when a patient is moved. Typically the battery backup includes rechargeable batteries, such as Nickel-cadmium (NiCd) batteries, to reduce the need to replace batteries and reduce operating cost. After the batteries are used, the batteries need to be recharged. Recharging the batteries draws additional current from the power supply and can be the major load on the power supply.
As the amount of current drawn through the power supply increases, the temperature of various components of the power supply increases. U.S. Pat. No. 5,712,795, to Layman et al., describes a method for monitoring the battery temperature and controlling the charging rate of the battery to extend the service life of the battery. However, this technique does not take into account other important components of the power supply.
For other power supply components, as the temperature increases, the maximum amount of power that can be supplied decreases. Therefore, a method and apparatus are needed to monitor the temperature of certain other components of the power supply and to adjust the amount of power supplied.
In view of the disadvantages of the related art, it is an object of the present invention to provide a power management system that monitors the temperature of selected components in a modular patient care system and adjusts the amount of power supplied based on the temperature.
In a power supply of a patient care system, a power management system monitors the temperature of an off-line switcher and adjusts the amount of current supplied by the off-line switcher to operate the off-line switcher within a range of temperature and power limits.
In particular, the power supply includes an off-line switcher with an external power input and an internal power output. A first temperature sensor is thermally coupled to the off-line switcher and outputs a first sensed temperature. A voltage sensor is coupled to the internal power output and outputs a sensed output voltage of the off-line switcher. A current sensor is coupled to the internal power output and outputs a sensed output current of the off-line switcher. A battery charger is electrically coupled to the off-line switcher and to a battery. A memory stores a power management procedure. A power supply processor executes the power management procedure. The power management procedure causes the power supply processor to determine an internal power load PS by multiplying the sensed output voltage VSby the sensed output current IS, and to determine a power rating PTEMP based on the first sensed temperature. The power management procedure causes the battery charger to reduce a charge rate of the battery based on the power rating PTEMP and the internal power load PS.
In another aspect of the invention, in a patient care system, at least one functional unit is mechanically coupled to an advanced interface unit. The advanced interface unit has a connector electrically coupling the functional unit. The advanced interface unit includes the power supply of the present invention which supplies power to the functional unit via the connector.
In yet another aspect of the invention, a method of managing power in a patient care system is provided.
In another alternate aspect of the invention, a computer program product for managing power in a patient care system is provided. The computer program product is for use in conjunction with a computer system. The computer program product has a computer readable storage medium and a computer program mechanism embedded therein. The computer program mechanism includes a power management procedure and instructions that periodically invoke the power management procedure. The power management procedure causes a battery to charge at a high charge rate, measures a temperature of an internal power source, determines a supplied power supplied by the internal power source at the high charge rate, determines a maximum allowable power for the first temperature, and causes the battery to charge at a low charge rate when the supplied power exceeds the maximum allowable power.
In this way, the power management system ensures that at least one component of the power supply, such as the off-line switcher, operates within temperature and power limits. Because the power management system adjusts the charge rate of the battery to prevent the off-line switcher from overheating and failing, the power management system helps to ensure that higher priority patient care functional units continue to receive power. In addition, the power management system provides a more robust power supply. By operating the off-line switcher within limits, the power supply prolongs the useful life of the off-line switcher and therefore of the power supply.